题目

Different weather makes people feel different. It influences (影响) health intelligence（ 智力） and feeling. In August, it is very hot and wet in the southern part of the United States. People there have heart trouble and other kinds of health problems during this month. In the Northeast and the Middle West, it is very hot at some times and very cold at other times. People in these states have more heart trouble after the weather changes in February or March.       The weather can also influence intelligence. For example, in a 1983 report by scientists, IQ ( 智商) of a gr如果x的3倍与5的和等于x的9倍与7的差，那么x的值是 ．